Electric heating system for ovens



Jan. 13, 1948. F. H. MCCORMICK ELECTRIC HEATING SYSTEM Foa ovENs 17,1940 4 Sheets-Sheet l Filed Feb.

\Q 3Q lill. NS

Jan. 13, 1948.

F. H. MCCORMICK ELECTRIC HEATING SYSTEM FOR OVENS Filed Feb. 17, 1940 4Sheets-Sheet 2 Jan. 13, 1948. F. H. MccoRM|cK 2,434,467

ELECTRIC HEATING SYSTEM FOR OVENS Filed Feb. 17, 1940 4 Sheets-Sheet 3mi; [g5 u N t I A I n 1 Q g s u N E N ,J N N Ii Q s' N C n i: w l z n AN l N f Illir asc C) dan Q fg; u

M sq ,$5

7,1m/ OR 5 'f/3am ATTORNEYS Jan. 13, 1948. F H, MCCORMlCK 2,434,467

ELECTRIC HEATING SYSTEM FOR OVENS Filed Feb. 17, 1940 4 Sheets-Sheet 4Patented Jan. 13, 1948 2,434,467 ELECTRIC HEATING SYSTEM FOR OVEN SFrancis H. McCormick, Dayton, Motors Corporation, corporation ofDelaware General Ohio, assgnor to Dayton, Ohio, a

Application February 17,1940, Serial No. 319,519

14 Claims.

This invention relates to a domestic appliance and more particularly toplural unit electric oven heating systems providing an automatic changefrom preheat to bake circuit arrangement.

It is an object of my invention to provide for a plural unit oven,improved oven heating circuits including an automatic control providingan automatic change from high heat in both the upper and lower portionsof the oven to a low heat in the upper portion and ahigh heat in thelower portion of the oven, and to so design the circuit and to so placethe thermostat control in the circuit that the disconnecting of only oneconductor by the thermostate control will safely deenergize the entireheating circuit.

It is another object oi' my invention to provide a simplified controlfor a plural unit electric oven providing an automatic change frompreheat to bake circuit arrangement.

It is still another objectof my invention to provide a plural unit ovencircuit arrangement, in which an upper unit is fed from a tap on thelower unit for baking, when a Control providing an automatic change frompreheat to bake circuit arrangement.

It is still another object of my invention to provide an electric ovenheating system in which a simple electro-thermal control holds thepreheat circuit closed and provides an automatic change to bake circuitarrangement under the control of the thermostat.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had to the accompanyingdrawings, wherein a preferred form of the present invention is clearlyshown.

in the drawings:

Fig. 1 is a view partly in section and partly diagrammatic of a two-unitelectric oven heating system including an automatic control embodyingone form of my invention; y

Fig. 2 is a top view of the control knob and dial as shown in Fig. 1,

Fig. 3 is a top view of the upper cam shown in Fig. l;

Fig. 4 is a top view of the lower cam shown in Fig. l;

Fig. 5 is a simple wiring diagram of the electrical circuits shown inFig. 1;

Fig. 6 is a view partly in section and partly diagrammatic of a modiedtwo-unit electric Oven heating system including a modified automaticmechanically interlocked control embodying another form of my invention;

(CI. B19-20) y Fig. 7 is a top view of the control knob and dial shownin Fig. 6;

Fig. 8 is a top view of the upper cam shown in Fig. 6;

5 Fig. 9 is a top Fig. 6;

Fig. 10 is a simple wiring diagram of the electric circuit shown in Fig.6;

Fig. 11 is a modified simple wiring diagram 1o showing a modiilcation oithe electric circuits and supply conductors shown in Fig. 6;

Fig. 12 is a view partly in section and partly diagrammatic of anothermodified two-unit oven heating system including another modiiled au- 15tomatic control embodied in my invention; and

Fig. 13 is a fragmentary view of the preheatu bake control similar tothat shown in Fig. 12, but in the latched position assumed at theinstant the control knob is turned to breil position.

Referring now to the drawings and more particularly to Fig. 1, there isshown an electric oven heating system for a two-unit oven designated bythe reference character 20 provided with an upper heating unit 2iprimarily for broiling, and a lower heating unit 25 primarily forbaking. Both the upper and lower units 22 and 24 are connected by asingle common con ductor 26 to a thermostat provided with a movablecontact 28 and a stationary contact 30. The stationary contact 30 isconnected by a conductor 32 to one conductor of a power source. Thecontacts 28 and 3D are opened and closed in accordance with thetemperature oi a thermostat bulb 34 which is located within the oven 20.These contacts are also employed to deenergize the entire system whenthe oven is not used.

The thermostat includes a housing d3 provided with an opening whichreceives a bushing 49 which is rigidly secured to the edges of theopening. This bushing 49 is interiorly threaded in order to receive inthreaded engagement, the threaded adjusting screw 41. The inner end ofthe screw 47 engages a stud 4|! which is attached to the expansible andcontractible diaphragm di. The interior of the diaphragm il is incommunicationA with a capillary tube l2 which in turn is incommunication with the inferior ci the bulb 34. A contractible andexpansible liquid is provided inthe bulb and the capillary tube 42 sothat upon expansion of the liquid as a result of the heat to which thebulb is subjected, the liquid will be forced through the tube into theexpansible and contractible diaphragm 55 means 4l.

view of the lower cam shown in A tip 39 is provided on the :face of Nthe diaphragm opposite the stud 48 to facilitate tact |89 as long as theheater remains ener the transmission of the expansive forces of thegiZed. The heater is preferably placed suffidiaphragm to the operatinglevers. ciently close to the bimetal 96 and has sufllcient The tip 38abuts a projection 44 upon the Opcapacity that it will rapidly heat thebimetal 96 erating lever 45. The operating lever 48 has a 5 and willalmost instantaneously hold the contact knife edge which is seated in anotch of a bearing 98 against the stationary contact |89. If desired,

bracket 48 secured to the wall of the housing 43. an electromagnet maybe substituted for the A light coil spring 45 is provided for keepingthe heater Ill and the bimetal strip be replaced by projection 44 inengagement with the tip 38. an armature biased to close the contacts 98and The other end of the operating lever 4B is provided 18 |8 I. with anaperture receiving the hooked end of a The other end of the heater isconnected toggle tension spring 53. The other end of the directly to theconductor 88. This then connects toggle tension spring 53 is hookedthrough an the conductor 88 through the heater the conaperture in acontact arm 55 which has its one tacts |89 and 98 and through thebimetal 9G and end provided with a knife edge held by a station- 15 theconductor 94 with one terminal of the upper ary notched support 51. Theother end of the unit 22 while the other terminal of the upper unitcontact arm 55 carries the thermostat contact 28 22 is connected throughthe conductor 25, the

through a spring connection. The movement vof contacts 28 and 38 withthe other supply conducthe contact arm 55 and the contact 28 away fromtor 32. Thus, in the preheat circuit arrangethe contact 38 is limited bya stop 56. 20 ment, the upper unit 22 is directly connected The screw 41is turned by an adjusting knob 48 across the supply conductors at fullvoltage, as is in order to set the thermostat to open and close thelower unit 24, which has its output reduced by at any desiredtemperature of the thermostat the change since no current is suppliedfrom the bulb 34. The knob 48 is fastened by a set-screw tap to theupper unit 22. The contacts 98 and 68 to a sleeve 82 which in turn isprovided with a 25 |88 will remain in engagement until the thermoplate64 carrying a slot which receives the pin 88 stat bulb 34 reaches thetemperature for which projecting from the screw 41. The plate 84 is theadjusting knob 48 of the thermostat is set. fastened to the sleeve 52 byscrews 88 which ex- At this temperature, the expansion of the tendthrough adjusting slots in the plate 84. The diaphragm 4| will separatethe contacts 28 and sleeve 62 rotates upon the outside of the bushing 3038, thereby deenergizing all circuits. This will 49 and carries anindicating dial 18. This sleeve deenergize the heater and allow thebimetal 62 also carries an upper cam 12 and a lower cam strip 96 tocool. Upon cooling, the contact 98 14, each cf which is fixed to thesleeve 52. will return to its engagement with the stationary The uppercam 12 actuates a push rod 18 which contact |8|, thereby restoring thesystem to the is normally held against the cam by a spring 18. 35 bakecircuit arrangement in which it will remain The other end of the pushrod 15 is adapted to during succeeding cycles of the thermostatconengage a spring strip 88 which is anchored at its tacts 28 and 38.Thus, in this simple way, an opposite end to an anchorage 82. Thisspring automatic change from preheat to bake circuit strip 88 isnormally tensioned to hold a movable arrangement is accomplished at theend oi' the contact 84 in engagement with a stationary con- 40 preheatcycle. This is performed without any tact 86. The closing of thecontacts 84 and 88 load upon the thermostat so that the sensitivityconnects the other conductor 88 of the supply of the thermostat is notaffected. Also, the source through the conductor 98, the contacts 85bimetal device is simple, noiseless and substanand 84 and through aconductor 92 to the other tially foolproof. terminal of the lower ovenheating unit 24. 45 For broiling, the upper and lower cams 12 and Forbaking purposes, the other terminal of the 14 respectively, are used toseparate the switch upper heating unit 22 is connected through thecontacts 84 and 86 and to close the contacts 88 conductor 94, thebimetal strip 98, the double conand |89. For this purpose, the cam 12 isprotact 98, stationary contact |8| and the conductor vided with a raisedor hump portion |2|. When |83 with a tap |85 upon the lower unit 24.This 50 the knob 48 is rotated to set the broll legend tap |85 dividesthe lower unit into sections 23 opposite the indicator for the dial 18,the raised and 25 and is so located in the lower unit 24 that or humpportion |2| of the cam 12 will engage the voltage which is applied tothe upper unit 22 and push outwardly the end of the rod 15 so that isjust sufficient to provide substantially uniform the spring strip 88will be deflected outwardly temperatures within the oven when the lowerunit 55 to separate the contacts 84 and 85. At thesame 24 is energizedat full voltage. Normally, this time, the lower cam 14 will be rotatedto place point should be so located that about one-third a recessedportion |23 in registration with a lower the full voltage is applied tothe upper unit 22. cam follower push rod |25 which extends through This,however, depends upon the resistance of the end of the bimetal strip 86and is provided the upper unit 22. With this arrangement, the 50 with acollar |21 on the far side and a collar |29 upper unit 22 is placed inparallel with section 23 on the near side. The movement of the lower andin series with section 25. The bimetal strip cam push rod |25 into therecess |23 under the 98 is so selected and formed that when it is atinfluence of the follower spring |3| causes the any room temperature thecontact 88 will be collar |21 to move the free end of the bimetal firmlyheld in engagement with the contact |8|. 65 strip 86 to the rlghtso thatthe contact 98 will For rapid1y bringing the oven to the desired be heldin engagement with the Stationary Contemperature prior to baking, a morerapid pretact |89.

heating circuit arrangement is provided. For This movement of the knob48 to the broil this purpose, the biinetal strip 96 is provided withposition thus connects the upper unit 22 across an operating knob |81 bywhich the bimetal strip 70 full voltage and disconnects the lower unit24 9E may be moved to place contact 98 in engageat the one terminal andalso its tap |85. The ment with the stationary contact |89. Theconcircuit for broiling includes the source conductact |89 is connectedto a heater which will tor 88, the heater the stationary contact heatthe bimetal strip 88 and cause the contact |89, the movable contact 98,the bimetal strip 98 to remain in contact with the stationary con- 7596, the conductor 94, the upper unit 22, the con- .y position forbroiling purposes.

I heating cycle.

ductor 26, the movable contact 28, the stationary contact 30 and thesource conductor 32. 'I'he knob 48 is turned sufilciently far to attainthe broil position that the thermostat; is set at a temperaturesuiiciently high to maintain the thermostat contacts closed for asufiicient length of time for broiling purposes. Ordinarily, the ovendoor is left open to prevent the oven temperatures from risingsufficiently high to open the thermostat contacts. kNo current ilowsthrough the lower unit 24 because the conductor 92 at its one terminalis disconnected by the opening of the contacts 84 and 86 and theconductor |03 which is connected to the top |05 is disconnected by themovement of the contact 98 away from the contact |l.

When the knob 48 is turned substantially 360 degrees in the oppositedirection to the "05 position, the upper cam 12 is turned so that asecond raised portion |33 will engage the upper cam push rod 16 to againopen the contacts 84 and 85. Likewise, the cam 14 will present a raisedportion |35 to the lower cam push rod |25 so that the shoulder |29 willengage the bimetal Strip 90 to separate the contacts 98 and |00, if theyshould happen to be engaged. This movement of the knob 48 to the "oifposition, will also open the thermostat contacts so that both sides ofall circuits will be disconnected from the source conductors. This willprovide positive assurance against any live conductors when the switchis turned to the off position.

However, this is not absolutely necessary, since the breaking of oneside of the line is suilicient in this circuit, since only two sourceconductors are employed. If desired, the push rod and its cam may beeliminated and thefknob |01 be used to move the bimetal element 90 topreheat position when the knob 48 is turned to the broil With such asystem, vthe bimetal 96 would naturally move when cooled to separate thecontacts 98 and |09, since the thermostat contacts 28 and 30 would beopen in the olf position. K

In Fig. 6 is shown a system in which the operation of the thermostat toopen position mechanically changes a double throw switch from preheat tobake" position at the end of the first In this form, the control knobdouble throw switch as well as andv broil circuit arrangements. In Fig.6, there is shown a two-unit oven designated by the reference character220 including an upper heating unit 222, primarily for broiling, and alower heating unit 224, primarily for baking. Both the-upper and lowerunits 222 and 224 are connected by a single common conductor 226 to athermostat provided with a movable contact 228 and a stationary contact230. The stationary contact 230 is connected by a conducsets the preheatprovides the bake ltor 232 to one conductor of a power source. The

contacts 228 and 230 are opened and closed in accordance with thetemperature of a thermostat bulb 234 which is located within the oven 220. 'Ihese contacts are also employed to deenergize the entiresystem'when the oven is not used.

The thermostat includes a housing 243 which rigidly supports the bushing249 which threadedly receives the control knob mechanism, similai tothat shown in Fig. 1. The rotation of the control knob 248/changes theposition of the inner end of the screw 241 which engages a stud attachedto the expansible and contractible 'diaphragm 24|.y The interior ofthejdiaphragm 24| is in communication with a capillary tube 242 theupper heating unit 222 which in turn is in communication with theinterior of the bulb 234, A contractible and expansible liquid isprovided in the bulb and the capillary tube 242 so that upon expansionof the liquid as a result of the heat to which the bulb is subjected,the liquid will be forced through the tube into the expansible andcontractible diaphragm means 24|.

A tip, provided upon the face of diaphragm 24| opposite the stud, abutsa projection upon operating lever 246. The operating lever 246 ispivoted at one end and is connected at the other end to a light togglespring 245 which has its other end connected to a pivoted contact arm255 carrying the movable contact 228. The contact cam by a spring 218.The other end of the pushl rod 210 is adapted'tofenga-ge'the spring'strip 280 contacts 284 and 2st connects the other conductor 288 of thesupply source to the other terminal of the lower oven heating unit 224through the conductor 290, the contacts 286 and 284 and the conductor292.

For banking purposes, therother terminal of is connected through aconductor 294, to a contact arm 296 carrying a double contact 298,normally in contact with a stationary contact 30| connected by theconductor 303 with a tap 305 upon the lower unit 224. This tap 305divides the lower unit into sections located in the lower unit 224 thatthe voltage applied to the upper unit 222 is just suflicient to providesubstantially uniform heating and uniform temperatures within the ovenwhen the lower unit 224,is energized at full voltage. In the normaloven, this point ordinarily falls so that the section 223 includes aboutone-third the total resistance of the lower unit 224. The contact arm296 is pivoted at the end opposite the double contact 298. and isprovided with a tension toggle spring 300 for keeping the double contact208 either in engagement with the stationary contact 30| or a stationarycontact 309.

For rapidly preheating the oven, theknob 243 is first turned to thebroil position; This brings into operation the lower cam 214 which, likethe upper cam 212, rotates with the knob 248. This lower cam 214'actuates a push rod 325 which is normally held against cam 214 by afollower spring 33|. Y

In order to provide an automatic preheat cycle prior to a normal bakingcycle, the knob 248 is rst turned to the broil position and thereafteris immediately turned back to the baking temperature desired. When theknob 248 is turned to the broil position, the cam 214 will present araised portion 323 to the adjacent end of the cam follower push rod 325.This will cause the cam surface 321 upon the push rod 325 to lift thevertical operating bar 329 until its hooked lower end raises the contactarm r296 across its dead center position so that the double contact 298will then move into and be held in engagement with the stationarycontact 309 by the toggle spring 300. This connects the one terminal ofthe upper unit 224 and the conductor 294 through the contact 298 and thecontact 309 directly to the source conductor 288 instead of the tap 305.This, therefore, will connect the upper unit 222 across full voltage,thereby greatly increasing its output for rapid preheating purposesprior to baking.

The contact 298 will remain in contact with the stationary contact 309until the thermostat bulb 234 reaches the baking temperature for whichthe adjusting knob 248 of the thermostat is set. At this time, thecontacts 228 and 230 will be separated and the contact arm 255 will movedownwardly carrying with it a pin 2 I 9 which will strike the contactarm 296 to separate the contact 298 from the contact 309 and to overcomethe force of the toggle spring 300 to move the double contact 298 intoengagement with the contact 30|. At this time, al1 the circuits of thesystem will be deenergized by the opening of the contacts 228 and 230.The contact 298 will remain in contact with the contact 30| throughoutthe succeeding cycles of the thermostat contacts 228 and 230 to maintainthe proper baking circuit arrangement of the upper and lower units forbaking purposes.

For broiling, the knob 248 is turned to the broil position and left inthat position for the duration of the broiling operation. As mentionedbefore, this will throw the contact 298 into contact with the stationarycontact 309 to connect the upper unit 222 directly across the supplyconductors 288 and 232. At the same time, the upper cam 212 will presenta raised portion 32| which will push the push rod 216 outwardly toseparate the contacts 284 and 286 to deenergize the lower unit 224. Inthe broil position, the thermostat is adjusted to a sufiiciently highoperating temperature to prevent cycling.

When the knob 248 is turned to the ofi position, the thermostat contacts228 and 230 will be opened and the contact arm 255 will cause the pin 2i 9 to engage the contact arm 296 to move the contact 298 again intocontact with the stationary contact 30|. However, the cam 212 isprovided with a second raised portion 333 which will push the push rod216 outwardly in the orf position of the knob 248, to separate thecontacts 286 and 284. This insures positive deenergization of the entiresystem.

The advantage of opening these contacts in the o position is illustratedin Fig. 11 in which the contact 30| is connected to a neutral (ground)conductor 302 instead of by the conductor 303 to the tap 805. Otherwise,the circuit shown in Fig. 11 is exactly like the circuit shown in Figs.6 and l0 and all the other elements are identical. However, it will beseen that by opening the contacts 284 and 286 as well as moving contact298 into Contact with the contact 30| and by opening the singlethermostat contacts 228 and 230 in the ofi position, all parts of thesystem are safely deenergized and only a single set of simple contactsis required for the thermostat, even though the three-wire Edisoncircuit is used as a source.

In Figs. l2 and 13, there is shown another modied form which issubstantially identical to the form shown in Figs. 1 to 5 excepting thatthe preheat is actuated as in Figs. 6 to 10 by first moving theregulating knob to the breil position and thence to the bakingtemperature desired, and excepting that a latch is also provided forinstantaneously holding the bimetal in prehea position until the bimetalis suiiiciently heated to remain in the preheat position.

Referring now more particularly to Figs. 12 and 13, there is shown acontrol knob 448 provided with an upper cam 412 and a lower cam 414which, through a primary lever 446 and a toggle spring 453, operates thepivoted contact arm 455 to open and close the thermostat contacts 428and 430. The thermostat contacts 428 and 430 connect the conductor 432with a conductor 426 which connects with one terminal of the heatingunit 422 and one terminal oi the lower heating unit 424. These terminalare located within an oven indicated diagrammatically and designated bythe reference character 420. The upper cam 412 operates a push rod 416to open the contacts 484 and 486 in the broil and oil positions of theknob 448. The knob 448 is provided with legends upon its dial as shownin Fig. 2. The contacts 488 and 484 connect the source conductor 488 andthe conductor 490 to the conductor 492 which connects to the otherterminal of the lower unit 424.

The double throw bake and preheat switch includes a bimetal element 496which carries a double contact 498. This bimetal element is so formedthat at ordinary temperatures, it normally holds the contact 498 inengagement with a stationary contact 50|. This connects the upperheating unit 422 with the tap 505 on the lower unit. The circuit for theupper unit 422 in the bake circuit arrangement thus includes the sourceconductor 432. the contacts 430 and 428, the conductor 426, the upperheating unit 422, the conductor 494, the bimetal element 496, contacts498 and 50|. the conductor 503, the tap 505, the section 425 of thelower unit 424, the conductor 492, the contacts 484 and 486, theconductor 490 and the source conductor 488.

For preheat purposes, the knob 448 is rst turned to the broil positionand then turned to one of the bakingy temperature positions. The turningof the knob 448 to the broil position causes the cam follower 525 toengage the recess on the cam 414 corresponding to the recess |23 in thecam 14 to retract the follower 525 under the influence of the followerspring 53| in order to cause the cam shoulder 521 to engage the bimetalelement 496 and to pull the bimetal element 496 into the position shownin Fie. 13 where the upper end of the bimetal 496 will ride over and becaught by the catch 55| on a second bimetal member 553 which is anchoredto the support 555. This will close a circuit which in cludes the sourceconductor 488. the conductor 559, an electric heater 551 for heatingYthe bimetal 553. a conductor 5|2, the electric heater 5| i,(corresponding to the heater of Fig. 1), the contact 509. the contact498. the bimetal element 496, the conductor 494 which connects to oneterminal of the upper heating unit 422 having its other terminalconnected to the conductor 426, the contacts 428 and 430 and the sourceconductor 432.

The bimetal 553 assumes a lower position when at room temperature asshown in both Figs. l2 and 13, but when heated by the electric heater551, it curls upwardly to the dotted position shown in Fig. 13, so thatthe bimetal 496 is unlatched. However, as long as the thermostatcontacts 428 and 430 and contacts 498 and 509 remain closed, the heater5| I will keep the bimetal 496 heated with the contact 498 in contactwith the stationary contact 509. However, when the thermostat controlbulb 434 connected to the di- `,the knob is turned to said upper heatingmeans reaches the temperature for which the knob 488 is set, thethermostat contacts 428 and 430 will open, thus deenergizing the entiresystem including the electric heater H. This will allow the bimetal 496to cool and to move the contact 498 into contact with the stationarycontact without interference from the catch 55| which is so constructedthat it will not cool as rapidly as the bimetal 496. For this purpose,the bimetal 553 may be made wider or of heavier metal or may haveadditional metal attached thereto in order to make it cool more slowlythan the loimetal 496.

When the control knob 448 is turned to the off position, the upper cam4'12 will separate the contacts 484 and 486, while the lower cam 414will move the push rod 525 outwardly to cause the shoulder 529 to engageand move the bimetal element 496 so that the contact 498 will bepositively held in engagement with the stationary contact 50|. Normally,after the first few seconds of the preheat cycle, the bimetal 553 willbe bent upwardly by the heat applied to it by the heater 551 so that thebimetal 496 may be moved at any time thereafter without interferencefrom the catch 55|. However, if the knob 448 should be returned to theoi position before the bimetal 553 is heated suiliciently when the knobhas been in preheat or broil position, the shoulder 551 upon the pushrod 525 will move outwardly and will engage a cam 56| provided upon theend of the bimetal member 553 so that the coaction of the cam surfaceupon the shoulder 52? with the cam 56! will raise the bimetal member553, thereby releasing the catch from the end of the bimetal member 496prior to the time the shoulder 525 engages the bimetal 595 to move itpositively to its baking position. Thus, the system provides a, singleknob control for all positions including the actuation oi a simplebimetal preheat balie switch which can be instantaneously latched inpreheat position. Also, in this system, all contacts are opened when the01T position so that complete safety is assured.

While the form of embodiment of the invention as herein disclosed,constitutes .a preferred form, it is to be understood that other formsmight be adopted, all coming within the scope of the claims whichfollow.

What is claimed is as follows:

l.. An electric oven heating system including an upper oven heatingmeans, a lower oven heating means, a thermostat switch mechanism forconnecting and disconnecting one terminalof-the upaphragm 441 v per andlower heating means to and from one conn ductor of an electrical powersource, said lower heating means being provided with a tap at anintermediate point thereon, switch means for connecting anddisconnecting the other terminal of to and from said tap, switch meansfor connecting and disconnecting said other terminal of said upperheating unit to and from a second conductor of said power source, meansfor connecting said other terminal of said lower heating means to saidpower source, and means controlled by said thermostat switch mechu anismfor disconnecting said other conductor of said source from said otherterminal of the upper heating means and connecting said other ter minalto said tap.

2. An electric oven heating system including an upper oven heatingmeans, a lower oven heating means, a thermostat switch mechanism forconnecting and disconnecting one terminal of the upper and lower heatingmeans to and from one conductor of an electrical power source, saidlower heating means being an intermediate point thereon, switch meansfor connecting and disconnecting the other terminal of said upperheating means to and from said tap, switch means for connecting anddisconnecting said other terminal of said upper heating unit to and froma second conductor of said power source, means for connecting said otherterminal of said lower heating means to said power source, and meanscontrolled by said thermostat switch mechanism for disconnecting saidother conductor of said source from said other terminal of the upperheating means and connecting said other terminal to said tap, means forclosing one of said switch means and opening the other to disnect saidother terminal of said upper heating means from said tap and connectingsaid other terminal to said second conductor of said power source, andmeans for disconnecting said other terminal of said lower heating meansfrom said second conductor of said power source for broiling purposes.

3. An electric oven heating system including an upper oven heatingmeans, a lower oven heating means, a thermostat switch mechanism forconv for connecting and disconnecting necting and disconnecting oneterminal of the upper and lower heating means to and from one conductorof an electrical power source, said lower heating means being providedwith a tap at an intermediate point thereon, switch means the otherterminal of said upper heating means to and from said tap, switch meansfor connecting and disconnecting said other terminal of said upperheating unit to and from a second conductor of said power source, meansfor connecting said other terminal of said lower heating means to saidpower source, means controlled by said thermostat switch mechanism fordisconnecting said other conductor of said source from said otherterminal of the upper heating means and connecting said other terminalto said tap, means for closing one of said switch means and opening theother to disconnect said other terminal of said upper heating means fromsaid tap and connecting said other terminal to said second conductor ofsaid power source, and means for simultaneously disconnecting said otherterminal of said lower heating means from said second conductor of saidpower source for broiling purposes.

4. An electric oven heating system including an upper oven heatingmeans, a lower oven heating means, a thermostat switch mechanism forconnecting and disconnecting one terminal of the upper and lower heatingmeans to and from one conductor of an electrical power source, saidlower heating means being provided with a tap at an intermediate pointthereon; a double throw switch having one contact connected to said tap,another contact connected to a second conductor of said source, and thedouble contact to said other terminal of said upper heating means, meansfor connecting the other terminal of said lower heating means to saidsecond conductor of said power source, and means controlled by saidthermostat switch mechanism lor operating said double throw switch.

5. An electric oven heating system including an upper oven heatingmeans, a lower oven heating means, a thermostat switch mechanism forconnecting and disconnecting one terminal of the provided with a tap atupper and lower heating means to and from one conductor of an electricalpower source, said lower heating means being provided with a tap at anintermediate point thereon; a double throw switch having one contactconnected to said tap, another contact connected to a second conductorof said source, and the double contact to said other terminal of saidupper heating means, means for connecting the other terminal of saidlower heating means to said second conductor of said power source, meansfor said double throw switch for normally holding it in one positionproviding a connection between said other terminal of said upper heatingmeans and said tap, and electrically operated means for holding saiddouble throw switch in a second position connecting said other terminaland said second conductor.

6. An electric oven heating system including an upper oven heatingmeans, a lower oven heating means, a thermostat switch mechanism forconnecting and disconnecting one terminal of the upper and lower heatingmeans to and from one conductor of an electrical power source, saidlower heating means being provided with a tap at an intermediate pointthereon; a double throw switch having one contact connected to said tap,another contact connected to a second conductor of said source, and thedouble contact to said other terminai of said upper heating means, meansfor connecting the other terminal of said lower heatingr means to saidsecond conductor of said power souice, means lor said double throwswitch for normally holding it in one position, providing a connectionbetween said other terminal of said upper heating means and said tap,and electricaliy operated means connected in series with said anothercontact for holding said double throw switch in a second positionconnecting said other terminal and said second conductor.

rI. An electixc oven heating system including upper and lower ovenheating means, control means having oiif preheat," "bake and broilpositions, said control means including means for disconnecting oneterminal of said lower heating means in oit and broil positions andconnecting said terminal to a source conductor in preheat" and bakepositions, said control means including a control device connected toone tei'- minal of the upper heating means and having a normal akeposition normally providing a bake circ 'f arrangement energizing bothheating mea with the lower heating means energiZed at a higher voltagethan the upper heating means, said control device also having aselective preheat position providing a preheat circuit arrangement inwhich the upper and lower heating means are energized at substantiallythe same voltage, said control means including a thermostatic device forchanging said control device from preheat to bake position, saidthermostatic device also including contacts connected to other terminalsof said upper and lower heating means.

8. An electric oven heating system including upper and lower ovenheating means, control means having ofi, preheat, bake and broilpositions providing preheat, bake and broil circuit arrangements oi theoven heating means in the respective positions and completelydeenergizing said heating means in the ofi position, said upper andlower heating means being both energized at full wattage in said preheatposition, said upper heating means being energized at reduced wattagewith said lower heating means at full wattage in bake position,

and said upper heating means alone being energized in broil position,said control means including a selective double throw switch mechanismfor changing the circuit arrangement from the preheat to bakearrangement and for selecting the preheat arrangement, said double throwswitch being connected to one terminal of said upper heating means andto one source conductor, said control means including another switchmeans connected to one terminal of said lower heating means and to saidone source conductor together with means for closing said an.. otherswitch in the bake and preheat positions and opening said another switchin the off and broil positions, said control means also including athermostatic switch for controlling the movement of the,double throwswitch to change the circuit arrangement from preheat to bake circuitarrangement, said thermostat switch having contacts connected to otherterminals of said upper and lower heating means and to another conductorof said source, said thermostat being movable to separate its contactsin the olf position.

9. An electric over system adapted to be connected to two lines of asource of electric power comprising a unitary upper heating resistance,a series sectional lower heating resistance, thermostatic switchmechanism having knob means adapted to be placed in oil temperatureadjustable bake, broil and preheat" positions and having two singlethrow single contact arms and a double throw single contact arm soactuated by said knob means that said resistances are disconnected iromsaid two lines in the off position, are placed in parallel across saidlines in "preheat position, are placed with the lower resistance acrosssaid lines and with the upper resistance across one of said lines and atthe junction of the sections of said lower heating resistance in thebake" position, and are placed with the upper heating resistance onlyacross the lilies in the broil position, the thermostatic switchmechanism automatically changing the setting from preheat, to bake atthe end of the preheating cycle.

10. An electric oven system adapted to be connected to two lines of asource of electric power comprising a unitary upper heating resistance,a series sectional lower heating resistance, thermostatic switchmechanism having knob means adapted to be placed in oil temperatureadjustable bake, broil and preheat positions and having two single throwsingle contact arms and a double throw single contact arm so actuated bysaid knob means that said resistances are disconnected fi'om said twolines in the oi position, are placed in parallel across said lines inpreheat position, are placed with the lower resistance across said linesand with the upper resistance across one of said lines and at thejunction of the sections of said lower heating resistance in the bakeposition, and are placed with the upper heating resistance only acrossthe lines in the broil position, the thermostatic switch mechanismautomatically changing the setting from "preheat" to bake at the end ofthe preheating cycle by means oi a heating device acting on one of saidarms.

l1. An electric oven system adapted to be connected to two lines of asource oi electric power comprising a unitary upper heating resistance,a series sectional lower heating resistance, thermostatic switchmechanism having knob means adapted to be placed in off" temperatureadjustable bake, broil and preheat positions and having two singlethrowsingle contact arms and a double throw single contact arm soactuated by said knob means that said resistances are disconnected fromsaid two lines in the off position, are placed in parallel across saidlines in preheat position, are placed with the lower resistance acrosssaid lines and with the upper resistance across one of said lines and atthe Junction of the sections of said lower heating resistance in thebake position, and are placed with the upper heating resistance onlyacross the lines in the broil position, the thermostatic switchmechanism automatically changing the setting from preheat to bake at theend of the preheating cycle by means of a snap action spring on one ofsaid arms actuated by another of said arms.

12. An electric oven system adapted to be connected to three lines of asource of electric power comprising a unitary upper heating resistance,a unitary lower heating resistance, thermostatic switch mechanism havingknob means adapted to be placed in oif, temperature adjustable bake andbroil positions and having two single throw single contact arms and adouble throw single contact arm so actuated by said knob means that saidresistances are disconnected from at least two of said lines in the offposition, are placed in parallel across two of said lines at relativelyhigh voltage upon manipulation from broil to bake positions, are placedwith the lower resistance across two of said lines at relatively highvoltage an-d with the upper resistance across one of said lines and theother of said lines at a relatively low volta-ge in the bake position,and with the upper resistance across two of said lines at relativelyhigh voltage in the brcil position, the thermostatic switch mechanismautomatically changing the setting of the two resistances in parallel atrelatively high voltage to the bake setting at the end of a preheatingcycle.

13. An electric oven system adapted to be connected to three lines of asource of electric power comprising a unitary upper heating resistance,a unitary lower heating resistance, thermostatic switch mechanism havingknob means adapted to be placed in off temperature adjustable bake, andbroil" positions and having two single throw single contact arms and adouble throw single contact arm so actuated by said knob means that saidresistances are disconnected from at least two of said lines in the offposition, are placed in parallel across two of said lines at relativelyhigh voltage upon manipulation from broil to bake positions, are placedwith the lower resistance across two of said lines at relatively highvoltage and with the upper resistance across one of said lines and theother of said lines at a relatively low voltage in the bake position,and with the upper resistance across two of said lines at relativelyhigh voltage in the broil position, the thermostatic switch mechanismautomatically changing the setting of the two resistances in parallel atrelatively high voltage to the bake setting at the end of a preheatingcycle by means of a snap action spring on one of said arms actuated byanother of said arms.

14. An electric heating means for heating a zone to be heated, singlepole thermostatic switch means for controlling the connection of theheating means to one live supply line of a power source to regulate thetemperatures of said zone, connecting means for Aconnecting said heatingmeans selectively into a baking circuit arrangement and into a preheatcircuit arrangement and including switch means controlling theconnection to another live supply line of said power source, manuallyoperable means having off and on positions for operating said connectingmeans to change from the baking circuit arrangement to the preheatcircuit arrangement in the on position and disconnecting said livesupplylines in the oi position, and electrically operated meansenergized in response to the opening of said thermostatic switch meansfor controlling the operation or" said connecting means to change fromthe preheat circuit arrangement to the baking circuit arrangement.

FRANCIS H. MCCORMICK.

REFERENCES CITED The following references are of recordin the le of thispatent:

